The goal of the proposed research is the further elucidation of the functional organization of the mammalian spinal cord, utilizing electrophysiological and morphological techniques. The emphasis will be on the spinothalamic tract in the monkey. The experiments will include anatomical work using the marker enzyme, horseradish peroxidase, further study of the receptive field properties of spinothalamic neurons to stimuli activating nociceptors, the effects of stimulation of brain structures known to produce analgesia, investigation of the pharmacology of spinothalamic neurons, and a study of the input from the spinothalamic tract to the thalamus and to other brain structures by way of collaterals. The work should have relevance to the field of pain mechanisms.